1. Field of the Invention
The present invention relates to a deformation sensor which is mounted on a vehicle and which can detect a collision and so on of a vehicle.
2. Description of the Related Art
An occupant protection system for protecting an occupant at the time of collision is equipped with automobiles. The occupant protection system comprises a sensor for detecting a shock, an occupant protection ECU (an electronic control unit) for judging whether or not a collision occurs based on a signal from the sensor and an occupant protection device such as an air bag and so on. Here, the sensor for detecting the shock includes, for example, an acceleration sensor for detecting an acceleration at the time of collision (appropriately, including a deceleration, the same applies to the following) (see Japanese Unexamined Patent Publication (KOKAI) No. 6-56000). Furthermore, a load sensor for detecting a load at the time of collision by using an optical fiber is included (see Japanese Unexamined Patent Publication (KOKAI) No. 2006-142876).
For example, when a vehicle collides with other vehicles and so on at the front, an acceleration occurs in a forward direction (a traveling direction) of the vehicle. Furthermore, when other vehicles collide with the vehicle from the side thereof, an acceleration occurs in a horizontal direction of the vehicle. The acceleration sensor detects an acceleration which is occurred, and the occupant protection ECU judges whether or not a collision occurs based on the value of the acceleration. Namely, according to the acceleration sensor, whether or not a collision occurs is judged from an acceleration indirectly. However, other than a shock, by a running condition such as, for example, running on a curb stone, running on a bad road and so on, an acceleration occurs. On this account, even when a collision doesn't occur, the acceleration sensor judges that a collision occurs by an acceleration which is occurred, and there is a fear that the occupant protection device malfunctions.
Furthermore, the acceleration sensor is normally disposed in a vehicle body with a dotted condition. Moreover, the acceleration sensor cannot detect an acceleration unless the acceleration sensor itself receives an acceleration. On this account, when a portion apart from the disposed position is partly came into collision and so on, an acceleration is hardly detected, and a collision cannot be recognized correctly.
On the other hand, in an optical fiber sensor, when an optical fiber is deformed by a collision, a loss of light which is transmitted from one end to the other end of the optical fiber increases. The occupant protection ECU judges whether or not a collision occurs based on the value of the loss of light. However, it is difficult to arrange optical fiber sensors in a wide range, and a wiring route becomes complicated. Especially, when the disposed place is a curved surface, an arrangement is difficult. Furthermore, as above described, the optical fiber sensor determines whether or not a collision occurs by using the deformation of the optical fiber. Here, a deformation amount of the optical fiber is relatively small. On this account, a detection range of the optical fiber sensor is relatively narrow. Moreover, when someone tries to detect a collision position by using the optical fiber sensor, a light-emitting source and a light-receiving source, both of which are independent respectively, are required depending on the detecting position. Consequently, the occupant protection system becomes expensive.